You know, I do believe that I have stumbled upon the 800lb gorilla in the room that kind of proves (as much as repeated historical events can ever prove something) that religion is not only not needed for a functioning society, but is actually anethma to it.
What single factor has provoked the vast majority of wars that mankind has ever fought? Religion.
Why is the ME such a hotbed of violence? Religion.
Why is Afghanistan and Pakistan such a horrible place for women? Religion.
I could go on, but you get my point.